Dental articulators are a common and necessary apparatus in the fabrication of a dental prosthesis. Stripped to its bare essentials, the process of fabricating a prosthesis commences when the dentist takes impressions of the patient's maxillary and mandibular arches which may or may not include some natural teeth. These impressions are negative imprints of the arches and become the molds into which the raw material for forming positive dental casts are poured. These positive casts are duplicates of the patient's arches (with or without teeth) and become the primary model to which the prosthesis is to be constructed.
In order to construct an acceptable prosthesis, these dental casts are normally mounted in a dental articulator in order that the maxillary and mandibular casts are maintained in the same anatomical relationship as in the mouth of the patient. This is true in all cases even those where only one prosthesis, as for example the maxillary arch is to be constructed, since the prosthesis must also conform with the relating surfaces on the mandibular arch in the patient's mouth.
Another reason why the dental casts are mounted in an articulator is to permit arrangement of the denture (false) teeth in their proper position for occlusion. On partial dentures, the occlusion of the denture teeth must be with natural teeth. On full dentures greater liberty is often taken to improve function and esthetics. The desired occlusion not only includes the vertical bite but also a degree of lateral movement as well as posterior and anterior movement of the lower jaw. These various movements are produced by the temporomandibular joint which is the joint formed by the condyle of the mandible and the temporal bone. Many dental articulators are built to simulate these movements to a high degree.
Past practice for countless years has been to mount the dental casts in the articulator by means of plaster which is usually a gypsum material. This locates the dental casts in a fixed position. Mounting the dental casts by means of plaster is relatively expensive, is dusty and time consuming because the powdered raw material must be thoroughly mixed with a liquid and the plaster must be allowed to set, the process is subject to error which cannot be compensated, and all utensils must be thoroughly cleaned after each use. Even in cases where the dental casts have been provided with grooves to facilitate removal and remounting which is often a requirement in the fabrication process, it is questionable at best whether or not the casts were remounted to their precise originally mounted positions.
At least 95% of all dental articulators built to date have been built for use with plaster mounting techniques. A few have been built which use mechanical mounting devices such as claws or other clamping devices in an attempt to find a better mounting technique than by the use of plaster. These alternate mounting techniques have been far less satisfactory than plaster, especially in those situations where the dental casts are to be removed and remounted to their original positions.
The above referenced U.S. Pat. No. 4,169,314 and U.S. patent application are the first known articulators mounting dental casts without the use of mounting plaster and having the required precision for the most exacting requirements in the fabrication of dental prostheses.
With the exception of the above referenced articulators, all prior known articulators which mounted dental casts by mechanical means in lieu of mounting plaster did so by means of clamping devices around the periphery of the dental casts. Their greatest weakness is their inability to permit removal of the dental casts from the articulator and then subsequently remounting the casts to their precise original position. This is an absolute requirement except for the more simple crown and bridge work. Although such articulators permit the mounting of dental casts in a relatively fast manner, their lack of precision is the primary cause for their low acceptance by the dental profession. The clamps all worked like a vise in which the dental casts were clamped. As the plaster of which the dental casts are made is mechanically abraded by the clamps, the position of the dental casts will shift in the articulator.
The above referenced articulators solved the problem by locating on fixed points such as the threaded aperture in the base of the dental casts, or by an embedded button having a threaded aperture. The holding or retaining means of these articulators do not disturb these fixed locating points and dental casts are easily remounted to their precise original position.
The present invention is a further simplification of the mechanical mounting of dental casts having fixed locating apertures in the base of the dental casts. Instead of using threaded apertures as in the above referenced articulators, the articulator of the present invention uses unthreaded apertures which are easier and faster to form. The dental casts may be poured in the same manner they have been poured for years (that is without threaded embedded buttons) and the apertures are easily formed in the dental laboratory on a dental lathe which is in every laboratory. One aperture is preferably a round aperture in the central portion of the dental cast and the second aperture is preferably a radial slot, each of the apertures to receive a locating pin protruding from a flat surface on the articulator. The central pin is the principal pin and prevents all movement of the dental cast except rotational movement. The pin engaging the radial aperture in the dental cast prevents rotational movement of the cast. It takes very little holding force to retain the dental casts in their mounted position. There are numerous methods by which the dental casts may be retained. One very simple and effective method is depicted in the drawings.